You are at a table for two, sitting with your girlfriend or boyfriend, when, for no good reason (you can't help it, you didn't mean to do it), you yawn. It's a big, gaping, jaw-extending, embarrassing yawn and because you didn't cover your face, oh, God, she/he sees it. A second or two goes by, and then ... something doesn't happen. Your girlfriend/boyfriend doesn't yawn back.

Should you be alarmed?

I ask because in his newest (about to be published) book, science writer Sam Kean has a startling idea about yawning and true love.

"Yawns," Kean writes, in The Tale of the Dueling Neurosurgeons, "are a rich neuroscientific subject." Lots of animals yawn. Snakes do it. So do dogs, birds, turtles, apes, monkeys. It's a very old reflex; but in people, yawns can be contagious. We can catch them and send them. That's rarer. Only humans, baboons, chimps and (sometimes) dogs do that.

Babies Can't Catch A Yawn

And humans, writes Kean, "don't pick up contagious yawning until [age] 4 or 5, implying that we need to develop certain parts of the brain first, probably related to social skills and empathy."

In 2011, researchers at the University of Pisa chose 109 men and women from different countries and carefully recorded their day-to-day activities, making special note of any contagious yawning.

They discovered that if you yawn in front of your closest relatives — your parents, brothers, sisters, children — that yawn is especially contagious. Chances are high that those family members will (carefully covering their faces) yawn back.

But if you yawn in front of a group of close friends, there will be fewer yawns in return. The contagiousness seems to drop as day-to-day familiarity and empathy decline.

Going the next step: When you face a group of casual acquaintances, or even strangers, the scientists reported, your yawn may lose most of its contagiousness. You might get only one (hand-covering) yawn-returner.

Timing also tells tales. The scientists noticed that yawns move more quickly from senders to catchers when relationships are close. The delay between yawn and response was shorter for acquaintances than for strangers, suggesting that the closer, more familiar, more attached you are to the potential "catchee," the more likely he or she will promptly return the yawn.

The lesson here is: If somebody is really into you, your yawn should boomerang right back — or so it seems. That got Kean thinking. Imagine you are back at the table for two, face to face with your girlfriend, at close range. You're crazy about her and things seem to be going fine. Then you yawn.

There's a pause. She's looking right at you.

And she doesn't yawn back. Or she takes four seconds longer than she did last month.

Call it "Sam's Yawn Delay Predictor." In a footnote at the back of his book, he wonders "if you could tell someone was falling out of love with you by timing their yawn delay."

It's an intriguing notion, and if you wish to add the spice of science to what you suspect is a flagging love affair, here's what you can do: If you sense your partner is losing interest, bring a stopwatch on all your dates, yawn, and start measuring. Let's see if Kean is right. Does increasing the yawn delay mean she's breaking up with you? Hey, as someone never said, "When your heart is breaking, try science."